Traveling wave electron discharge devices



June 7, 1960 A. e. PEIFER TRAVELING WAVE ELECTRON DISCHARGE DEVICES Filed Dec. 3, 1954 9 25 1 MAM/MAR 3, /0

aecrm ,2 GUN INVENTOR ALEERT G. Pf/FEA 729/447 ATTORNEY United States Patent TRAVELING WAVE ELECTRON DISCHARGE DEVICES Albert G. Peifer, Nutley, NJ., assignor to International Telephone and Telegraph Corporation, Nutley, N.J., a corporation of Maryland Filed Dec. '3, 1954, Scr. No. 472,925

13 Claims. (Cl. 315-35) This invention relates to traveling wave electron discharge devices and more particularly to transition arrangements for matching a low impedance waveguide to the relatively high impedance waveguiding structure usually employed in such devices.

In the copending applications of I. H. Bryant, Serial No. 312,155, filed September 29, 1952, now U.S. Patent No. 2,794,145, R. E. White, Serial No. 312,083, filed September 29, 1952 now U.S. Patent No. 2,794,144, and.

R. E. White et al., Serial No. 471,412, filed November 26, 1954, now abandoned, certain forms of transition arrangements are disclosed which provide for impedance matching between the end of the high impedance helical transmission line and the relatively low impedance radio frequency terminal connections of a traveling wave electron discharge device or tube. In the aforesaid copending applications, the transition arrangements are disposed transversely of the axis of the helix and made in such form as to require but a small fraction of an inch of space measured in an axial direction. These matching arrangements thus reserve substantially all the available space between the source of electron beam supply and the electron collector for the helical line.

The impedance matching arrangements of the first two copending applications include parallel transmission line sections, the lengths of which are frequency dependent while the latter copending application includes a series transmission line section, the radial dimension of which is frequency dependent. The traveling wave tubes employing these impedance matching arrangements will have a diameter dependent upon the frequency at which the tube is operating and in certain instances this diameter may be quite large.

It is one of the objects of this invention to provide still another form of transition arrangement which also re quires very little axial space and which will enable the diameter of a traveling wave tube to be substantially smaller than a traveling wave tube employing the previous transition arrangements.

Another object is to provide transition sections for precise matching of a low impedance radio frequency coaxial terminal connection to a high impedance helical line.

One of the features of this invention is the structural arrangement of the transition section, that is, the special shaping of certain of the conductors thereof so as to provide gradual transition from the size of the outer conductor of the coaxial terminal connection to the smaller conductor size of a helical line and for cooperation in the impedance matching function. This is accomplished by tapering the width of the transition section.

Another feature of this invention is the provision of a specially designed strip conductor in conjunction with a cylindrical conductor for transmission of radio fre- .of an embodiment of the present invention.

I 2,939,992 Patented June 7, 1961) ice quency energy between the terminal connections and the helical line by providing the strip conductor in the form of a spiral spaced from the cylindrical conductor by a dielectric medium, the spacing therebetween being radially tapered between the point of coupling with the terminal connection and the helical line for cooperation in matching the impedances of said connection and said helical line.

Still another feature of this invention is .the provision of a spiral strip conductor in conjunction with a cylindrical conducting surface wherein the strip conductor and the cylindrical conducting surface are coupled together at one point to establish a radio frequency voltage null, said coupling together being capacitive in nature and the point of coupling being variable along a given are of the cylindrical conducting surface to enable the selection of a predetermined frequency of operation Within a given range of operating frequencies for a traveling wave tube.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a fragmentary view in longitudinal section of a traveling wave electron tube incorporated in transition sections at the ends of a helical line in accordance with the principles of this invention;

Fig. 2 is a cross-sectional view of the transition section of this invention taken along line 2-2 of Fig. 1; and

Fig. 3 is a cross-sectional view of an alternative embodiment of the transition section of this invention.

Referring to Fig. 1 of the drawing, a longitudinal section of the pertinent parts of a traveling wave electron discharge device is shown together with an illustration The tube generally comprises an electron gun unit 1 for producing a beam of electrons for flow axially of the tube to a collector 2. The electron gun unit is either spaced from or made contiguous to an alignment or partition plate 3 which is positioned crosswise vacuum envelope 4 against abutment 5 on the inner surface thereof. Envelope 4 preferably is composed of a non-magnetic metallic material in the embodiment presently being discussed, but it is to be understood that the vacuum envelope may be composed of dielectric'material which has disposed concentrically therewith a non-magnetic metallic cylinder as disclosed in the cross-sectional view of Fig. 3. Carlied on the outer surface of the envelope 4 of the cylinder shell 6 of Fig. 3 is either a permanent magnet or magnetic coil-7 which serves to produce a magnetic field axially of the envelope 4. At the rear of the envelope is a second alignment or partition plate 8. Interposed between these two plates 3'and 8 is a radio frequency propagating structure 9 in the form of a helical trans-.

mission line, the line being supported by dielectric rods 10 or by a dielectric tube, whichever is desired. Any suitable dielectric, such as glass or quartz may be employed. The rods or tubing are supported on the plates 3 and 8 in openings 11 and 12. The helical line 9 is connected between the input and output radio frequency terminal connections 13 and 14 by means of transition arrangements or sections 15 and 16, respectively.

The transition section 15, for example, comprises a transmission line arrangement of the line-above-ground type which includes the envelope 4 as one of the. couductors and a strip conductor 17 as the other conductor wherein conductor 4 provides a reference or ground plane separated from the strip conductor 17 by a suitable dielecshown herein to be vacuum but may comwise coupled to the helical line 9. By making the strip conductor equal 'approximately to a quarter wavelength long or an odd multiple. thereof overthe operating frequency range ofthe traveling'wa've tube, the 'secti0n 15 becomes resonant. and thereby establishes a standing wave with a voltage null'at theshort. 19 and a voltage maximum at theend coupled to the. helical line 9. Theouter conductor 20 of the input radio frequency terminal con nectionli isconnectedto'envelope 4 and the inner confacsaoaa- 4 tween the strip conductor-17 and the cylindrical conducting surface of envelope 4. p

A spointed out hereinabove, the tapering of the width of strip 17 enables a transition between the size of the center conductor 21of connection 13 and the size of the conductor forming helical line 9 and also cooperates in the desired impedance match. This tapering of the width of strip, 17 as indicated at 25 also aids in obtaining a wide bandwidthsin the transition section 15, the bandwidth of which should be as large as the bandwidth of the remaining portions of 'thejtraveling wave tube. V

In the aforementionedi copending applications, there was disposed about the transition sections, a shielding arductor' 21 isconnected to the strip-conductor 17. The

connection between inner conductor 21 and strip 17 may be p'rovided by a conductor 22 brazed or otherwise bonded .to conductor' 17 and projecting through an aperture'in envelope '4' which makes electrical contact with inner conductor 2'11by means of socket 23. The aperture through which conductor .22 passes through envelope 4 is sealed for vacuum purposes by the dielectric seal '24. The connection to strip conductor 17 isrlocated at a point between the voltage null (minimum impedance), and vthe'voltage maximum (maximum impedance) points'so as re provide. a proper impedance matchbetween the impedance helical line 9 and the low impedance coaxial'connection 13. ,In order to provide a gradual transition and thereby avoid discontinuities to flow of radio frequency energy between the width of the strip 17 at thec'onnection to the coaxial line 13 and the size of the helical conductor, the strip is tapered as indicated The transition coupling 15 inFigs. 1 and 2 provides for the'propagation of radio frequencye'nergy from .the

coaxial connection 13 to the helical line 9 by means of a concentric-like strip-aboveground type transmission .line

comprising the spiral strip 17"and the cylindrical conductor' surface of envelope 4. The transition section 16 rangement-to eliminate any radiation which: may occur from the transmission sectionand whichmight interfere in the desired operation of the traveling wave tube. The radiation problem when employing aitransiti'on arrangement of the type herein described is substantially elimi nated by dimensioning the envelope 4 to have a diameter of such a value that this envelope or outer cylinder functions as a waveguidebeyond cutoff for the operating frequency of the device. lf this is done, radiation in either direction from the'transition'arrangement is eliminated. By employingthis cylinder as the envelope 4 as hereinabove proposed, the. overall diameter of the traveling wave tube maybe substantially decreased. Likewise, by employing the coaxial vacuum seal 24 of Figl, the

number of parts in the vacuum envelope can be decreased 'wave tube within a given operating frequency range. As

mentioned hereinabove with respect'to Fig; l, the envelmac 4 thereof could be ceramic rather than metallic.

is identical tothe form shown in 15, the, propagation,

fhowever, being in the reve'rse direction of the transition section.

The strip conductor 17 spaced. a'small fraction of, a

.quarterfwavelengthfiom the cylindrical conducting sur: face of the envelope 4sprovides for the propagation of a mode approximating the TEM mode. The strip17 is preferably of a width' suificient to provide satisfactory coupling to the coaxial transmission line, the portion disposed hetween'this coupling and the helicalline being 1 fco'operate' in' the impedance transition between helical line 9 and connection 13. The dimension h for the strip 17 over jthepcylindrical conducting surface of envelope 4 may 'be obtained fromithe expression Thus, in Fig. 3, it is proposed that envelope 4a be formed from a suitable dielectricmaterial, such as quartz or glass, which has disposed .thereabout in a concentric relation conductive cylinder 6 to function as the ground plane of the concentric-like strip-above-ground type transmission [line for utilization in the transition arrangement of this electromagnetic waves from the coaxial connection 13 in V where h is the spacingof the strip from the cylindrical surface, d the width of the strip 17 and s isthe dielectric constant of the dielectric material disposed between the strip and" the cylindrical surface. As ,will be obvious from the above expression, if the dimension h is varied between the point of contact with the connection 13, and the connection to'helix 9, there has then been introduced invention. Strip conductor 17a is coupled to conducting cylinder 6 capacitively to .provide a resonant transition section as disclosed in connection with Figs. 1 and 2. Portion 26 of strip conductor 17a 'eifectively is one plate of a capacitor While sliding element 27 forms the other plate of a capacitor with the dielectric material of envelope 4a functioning as the dielectric material disposed therebetween. This structurejarrangernent provides a capacijtiveshort for radio frequency wavesbetweencylinder 6 and strip"17a.. Sliding element 27 is in slidable contact witha portion of cylinder 6 over asmaller arc thereof. Element 27 may be moved by handle 28 in' slot 29 to change the location of the short .or coupling between strip 17a and cylinder 6. such that the resonant length of strip 17a maybe varied over'a small range to enable the selection of a particular frequency of operation within a given frequency range. The. remaining c0nsidera tions of the transition section of Fig. 3 areidentical to that illustrated in Figs. 1 and 2:and disclosed hereinabove with respect thereto.

, The .arc through which sliding element 27 may be moved, and thereby the range offrequency selection, is

determined by thelength of element 27 and slot 29. This comes about .by the fact that if slot 29 is not covered by sliding element 27 a radiation through slot 29 will occur.

' Thus, the slot 29 must be covered at all times and in all positions of element 27 by element 27 to prevent undesired radiation from the traveling wave tube'through slot 29. Thisradiation consideration,"therefore, restricts the number of frequencies which may be selected from a given rangeofsoperating frequencies.

. 'Whilelhave described above the principles'of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. In a traveling wave electron discharge device having a radio frequency wave propagating structure of relatively high characteristic impedance and a radio frequency transmission line of relatively low characteristic impedance; a transition section coupling said low impedance line to said propagating structure comprising a first conductor substantially concentric with the longitudinal axis of said propagating structure, a second conductor spaced radially from said first conductor having a substantially spiral-like configuration about said longitudinal axis, said first and second conductors forming a transmission line spaced radially from and disposed about an end of said propagating structure, means coupling said first and second conductors together at one point to establish a radio frequency voltage null, the length of said transmission line from said voltage null measured circumferentially therealong providing a resonant section resonant at approximately the operating frequency of said device, said transmission line having a high radio frequency voltage portion disposed adjacent said propagating structure, means connecting said high voltage portion to said propagating structure, and means to couple said low impedance line to said first and second conductors at a point between said voltage null and said high voltage portion to match the impedance of said low impedance line.

2. In a traveling Wave electron discharge device having a radio frequency Wave propagating structure of relatively high characteristic impedance and a radio frequency transmission line of relatively low characteristic impedance; a transition section coupling said low impedance line to said propagating structure comprising a first conductor substantially concentric with the longitudinal axis or" said propagating structure, a second conductor spaced radially from said first conductor having a substantially spiral-like configuration about said longitudinal axis, said first and second conductors forming a transmission line spaced radially from and disposed about an end of said propagating structure, means coupling said first and second conductors together at one point to establish a radio frequency voltage null, the length of said transmission line from said voltage null measured circumferentially therealong providing a resonant section resonant at approximately the operating frequency of said devi e, said transmission line having a high radio frequency voltage portion disposed adjacent said propagating structure, means connecting said high voltage portion to said propagating structure, means to couple said low impedance line to said first and second conductors at a point between said voltage null and said high voltage portion to match the impedance of said low impedance line, and said second conductor being tapered from the point or" coupling to said low impedance line to the point of connection to said propagating structure.

3. in a traveling wave electron discharge device having a radio frequency Wave propagating structure of relatively high characteristic impedance and a radio frequency transmission line of relatively low characteristic impedance; a transition section coupling said low impedance line to said propagating structure comprising a first conductor substantially concentric with the longitudinal axis of said propagating structure, a second conductor spaced radially from said first conductor having a substantially spiral-like configuration about said longitudinal axis, said first and second conductors forming a transmission line spaced radially from and disposed about one end of said ro a atin structure, ca acitive means coupling said first and second conductors together at one point to establish a radio frequency voltage null, the

length of said transmission line from said voltage null measured circumferentially therealong providing a resonant section resonant at approximately the operating frequency of said device, said transmission line having a high ratio frequency voltage portion disposed adjacent said propagating structure, means connecting said high voltage portion to said propagating structure, and means to couple said low impedance line to said first and second conductors at a point between said voltage null and said high voltage portion to match the impedance of said low impedance line.

4. In a traveling wave electron discharge device having a helical propagating structure of relatively high characteristic impedance and a radio frequency transmission line of relatively low characteristic impedance; a transition section coupling said low impedance line to said helical structure comprising a cylindrical conducting surface substantially concentric with the longitudinal axis of said helical structure, a strip conductor spaced radially from said surface having a substantially spiral-like configuration about said longitudinal axis, said surface and said strip forming a transmission line spaced radially from and disposed about an end of said helical structure, means coupling said surface and said strip together at one point to establish a radio frequency voltage null, the length of said transmission line from said voltage null measured circumferentially therealong providing a resonant section resonant at approximately the operating frequency of said device, said transmission line providing a voltage maximum point at a distance of approximately a quarter Wavelength of said operating frequency from said null point, means coupling said low impedance line to said surface and said strip at a point between said null and said maximum point to match the impedance of said low impedance line, means to connect said strip in the region of said voltage maximum point to said helical structure, said strip being tapered from the point of coupling to said low impedance line to the point of coupling to said helical structure.

5. A transition coupler for use between a low impedance transmission line and a high impedance transmission line comprising a first conductor substantially concentric with a given axis, a second conductor spaced radially from said first conductor having a substantially spiral-like configuration about said given axis, said first and second conductors forming a transmission line, means coupling said first and second conductors together at one point to establish an impedance minimum, the length of said transmission line from said impedance minimum measured circumferent-ially therealong providing a resonant section resonant at a given frequency, said transmission line having an impedance maximum point at a distance approximately one quarter wavelength of said given frequency from said impedance minimum point, means coupling said low impedance line to said first and second conductors at a point between said minimum and maximum impedance points, and means to connect saidsecond conductor in the zone of said maximum impedance to said high impedance line.

6. A transition coupler for use between a low impedance transmission line and a high impedance transmission line comprising a first conductor substantially concentric with a given axis, a second conductor spaced radially from said first conductor having a substantially spirallike configuration about said given axis, said first and second conductors forming a transmission line, means coupling said first and second conductors together at one point to establish an impedance minimum point, the length of said transmission line from said impedance minimum point measured circumferentially therealong providing a resonant section resonant at a given frequency, said transmission line having an impedance maximum point at a distance of approximately one quarter wavelength of said given frequency from said minimum point, means coupling said low impedance line to said first and second conductors at a point between said impedance minimum and impedance maximum points -'-to matchthe in'ipedance of said lowi impedance line, means connecting said second-conductor in the regicnrof said f impedance maximum point to said high impedanee'line, and said second conductor being tapered from; the point ofc ou'plingto said :low impedance line to the point-of couplingto said high impedance line:

" i Atransition' coupler for use between a' low'impedance transmission line and a high impedance transmission line comprising a first conductor substantially concentric "with a given axis, a second conductor spacedradially from s'aid first'conductor having asubstantially spiral-like configuration about said' given axis; said first and second conductors forming a transmission 1ine,'rnean's coupling said firstand second conductors together at a point to,

establish an impedanceminimum point, the length of frequency from said impedance minimum point, means coupling saidlow impedance line to said conductors at a 7 point between said impedance minimum and impedance maximum points,"mean'sconnecting s'aidsecond conductor a v in, the, region of said impedance maximum impedancepoint to said high impedance line, and said first conductor has a diameter of-appropriate value to impart to said first conductor the characteristic of a Waveguide'beyond 'cutoif for said given frequency.

8.-A transition coupler for impedance matching 'bev 8 the reg cn vct a d mped n e m m po nt t s d highimpedance'line. a

lOV-A traveling wave electron discharge device comprising a metallic envelope, means'to project an electron beam along a path axially of said envelope, a radio frequency wave propagating structure of relatively high characteristic impedance disposed coaxially of said path, a radio frequency wave input terminal connection of relatively low characteristic impedance, a radio frequency wave output terminal connection of relatively low characteristic impedance, artransition sectioncoupling said input connection to the end of said propagating structure adjacent said means to project for the propagation of radio frequency wave therealong for interaction with the electrons of said beam, and a transition section coupling said output connection to the other end of said propagating-structure for removal of the interacted radio frequency waveethereirom, each of said transition sections including said envelope and a conductor spaced radially from said envelope having a substantially'spiral-like config uration'about the axis of said envelope, said envelope 7 and said conductor forming a transmission line spaced radially from and disposed about the respcctive end of -said propagating structure, means coupling said envelope and said conductortogether at one point to establish a radio frequency voltage null','the length of said transmis- 'sion line from said voltage null measured circumfertween a low impedancejtransmission lineand a high impedance transmission linecomprising'a cylindrical conducting surface substantially concentric to a gixenaxis, a-strip conductor spaced radially from said surface having a substantially spiral-like configuration 'about said givenhaxis, said conducting surface and said strip conlductorrforming a transmission line, means 'eouplingsaid *conducting surface and said strip conductor together at one point'to establish an impedance minimum point, the

length of said transmission line from said impedance minimum point measured circumferentially therealong providing aresonant section resonant at a given frequency, 7

said transmission line having an impedance maximum point at a distance of'approximately one quarter wavelength of said given-frequency from said impedance min imum point, means. coupling said low impedance line to said'surface and said strip at a point between said'impedance minimum and impedance maximum points to match the impedance of said low impedance line, and means connecting said strip in the region of said maximum impedance point to said high impedance line.

9. A transition coupler for'irnpedance matching be tween 2. low impedance transmission line and a'high impedance transmission line'comprising a cylindrical conducting surface substantially concentric to a given axis, a

strip conductor spacedradially from said surface having a substantially spiral-like con-figuration about said given axis, said conducting surface and said stripconductor forming a transmission line, capacitive means coupling said surfaceand said strip togetherat one point to estahlish an impedance minimum point,-the length of said transmission line from said impedance minimum point measured circumferentially therealong providing a resonant section resonant at a given frequency, said transmission line having'an impedance maximum point at a distance of approximately one quarter wavelength of said given frequencyfromsaid impedance minimum point,

' theimpedance of said transmission line steadily increasing :be'tween said impedance minimum point to said"imped- V -ance maximum point means coupling said lowiirnpedance line to said surface and said strip conductor at a 'givenpoint between said impedance minimum and inifpedance maximum points to'match the impedance of said -nection to said envelope and, said'conductor at a' point :between said voltage null and said high voltage portion to match the impedance of said terminal connection.

1 1'. A device according to claim 10, wherein the diam- V eter of said envelope is such as to establish said envelope as a waveguide beyond cutoff for the operating frequency of said device and the inner surface of said envelope defines a cylindrical conductive surface and said conductor includes a strip of conducting material separated from said cylindrical conducting surface by a dielectric medium V 2. A device according to claim 11, wherein said strip 'includes-a portion tapered from the point of coupling to said terminal connection and the-point of connection to said-propagating structure. 7 V V 13. A traveling wave electron dischargeedevice comprising a vacuum envelope of dielectric material, means to project an electron beam along a path axially'of said envelope, a helical radio'frequency wave propagating structure of relatively high characteristic impedance disposed coaxially of said path, a radio frequency wave input terminal connection of relatively low characteristic impedance, a radio frequency Wave output terminal connection of relatively low characteristic impedance, a transition section coupling said input connection to the end of said helical structure adjacent said means to project for launching radio frequency waves on said helical structure for interaction with the electrons of said beam, a transition section coupling said output connec- -tion to the other end of said helical structure for removal of the interacted radio frequency wave therefrom, and a metallic sleeve disposed in concentric spacedrelation to said envelope, each of said transition sections including said sleeve and a conductor spaced radially from said sleeve having a' substantially spiral-like configuration about the axis of said envelope, said sleeve and said constructure, movablemeans disposed adjacent said envelope to capacitively couple together said conductor and said sleeve at one point to establish a radio frequency voltlow impedance line, andmeans connecting said strip 7; age null, the length of said transmission line from said voltage null measured cireumferentially therealong being voltage null and said high voltage portion to match the adjusted by the positioning of said movable means to impedance of said terminal connections.

provide a resonant section at a selected frequency in the operating frequency range of Said device said transmis References Cited 111 the file of this patent sion line having a high radio frequency voltage portion .5 UNITED STATES PATENTS disposed adjacent said propagating structure, means con- Re. 23,647 Lindenblad Apr. 21, 1953 nesting said high voltage portion to said propagating 2,712,614 Field July 5, 1955 structure, and means to couple said terminal connections 2,727,179 Lally et a1 Dec. 13, 1955 to said conductor and saidsleeve at a point between said 2,774,006 Field et a1 Dec. 11, 1956 

